Comparative Study of Hydrogen Yield from Organic-Rich Lithologies: Implications for Sustainable Energy

Abstract The growing global demand for clean and sustainable energy has increased interest in hydrogen as an alternative fuel that is both affordable and widely accessible. While substantial research has focused on hydrogen generation through serpentinization, the potential of organic-rich systems remains largely unexplored. Addressing this gap requires systematic analysis of various organic-rich materials such as shale, carbonate rocks, and coal to evaluate their capacity to release hydrogen gas under different geological conditions. Such investigations could significantly advance our understanding of their roles in natural hydrogen systems. This study investigates the hydrogen generation potential of selected organic-rich rock samples through pyrolysis experiments conducted under controlled laboratory conditions. The samples were analyzed using X-ray diffraction (XRD), X-ray fluorescence (XRF), Rock-Eval pyrolysis, Thermogravimetric analysis (TGA), and Fourier transform infrared (FTIR), while the evolved gases were analyzed using gas chromatography (GC). Hydrogen yields ranged from 0.22 to 0.71 mg/g rock, with TOC-normalized yields between 4.2 and 29.4 mg/g TOC for all of the samples. Shale exhibited the highest hydrogen index (HI) of 885 mgHC/gTOC and contained type II kerogen, while coal, despite its high TOC of about 30.71%, produced lesser hydrogen gas with an HI of 387 mgHC/gTOC. TGA and FTIR analyses confirmed the progressive decomposition of organic functional groups associated with the release of hydrogen-rich gases. These findings suggest that organic-rich sedimentary formations, particularly those overlain by low-permeability caprocks such as tight shale, mudstone, or evaporites, may contribute to natural hydrogen systems and support hydrogen retention under favorable geological conditions.